How can I create a temp file with a specific extension with NET

Question

I need to generate a unique temporary file with a  csv extension   What I do right now is   string filename   System IO Path GetTempFileName   Replace   tmp     csv      However  this doesn t guarantee that my  csv file will be unique   I know the chances I ever got a collision are very low  especially if you consider that I don t delete the  tmp files   but this code doesn t looks good to me   Of course I could manually generate random file names until I eventually find a unique one  which shouldn t be a problem   but I m curious to know if others have found a nice way to deal with this problem

User · Answer

I think you should try  this   string path   Path GetRandomFileName    path   Path Combine   c  temp   path   path   Path ChangeExtension path    tmp    File Create path     It generates a unique filename and creates a file with that file name at a specified location

User · Answer

You can also do the following  string filename   Path ChangeExtension Path GetTempFileName      csv      and this also works as expected  string filename   Path ChangeExtension Path GetTempPath     Guid NewGuid   ToString      csv

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Try this function      public static string GetTempFilePathWithExtension string extension      var path   Path GetTempPath      var fileName   Guid NewGuid   ToString     extension    return Path Combine path  fileName       It will return a full path with the extension of your choice    Note  it s not guaranteed to produce a unique file name since someone else could have technically already created that file   However the chances of someone guessing the next guid produced by your app and creating it is very very low   It s pretty safe to assume this will be unique

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Easy Function in C    public static string GetTempFileName string extension    csv         return Path ChangeExtension Path GetTempFileName    extension

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The MSDN documentation for C   s GetTempFileName discusses your concern and answers it      GetTempFileName is not able to guarantee that the file name is unique       Only the lower 16 bits of the uUnique parameter are used  This limits GetTempFileName to a maximum of 65 535 unique file names if the lpPathName and lpPrefixString parameters remain the same       Due to the algorithm used to generate file names  GetTempFileName can perform poorly when creating a large number of files with the same prefix  In such cases  it is recommended that you construct unique file names based on GUIDs

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This is what I am doing    string tStamp   String Format   0 yyyyMMdd HHmmss    DateTime Now   string ProcID   Process GetCurrentProcess   Id ToString    string tmpFolder   System IO Path GetTempPath    string outFile   tmpFolder   ProcID         tStamp     txt

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This seems to work fine for me  it checks for file existance and creates the file to be sure it s a writable location  Should work fine  you can change it to return directly the FileStream  which is normally what you need for a temp file    private string GetTempFile string fileExtension      string temp   System IO Path GetTempPath      string res   string Empty    while  true        res   string Format   0   1    Guid NewGuid   ToString    fileExtension       res   System IO Path Combine temp  res       if   System IO File Exists res           try           System IO FileStream s   System IO File Create res           s Close            break                catch  Exception                         return res       GetTempFile

User · Answer

How about   Path Combine Path GetTempPath    DateTime Now Ticks ToString           Guid NewGuid   ToString       csv     It is highly improbable that the computer will generate the same Guid at the same instant of time  The only weakness i see here is the performance impact DateTime Now Ticks will add

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Guaranteed to be  statistically  unique   string fileName   System IO Path GetTempPath     Guid NewGuid   ToString       csv       To quote from the wiki article on the probabilty of a collision         one s annual risk of being hit by a   meteorite is estimated to be one   chance in 17 billion  19   that means   the probability is about 0 00000000006    6    10-11   equivalent to the odds of   creating a few tens of trillions of   UUIDs in a year and having one   duplicate  In other words  only after   generating 1 billion UUIDs every   second for the next 100 years  the   probability of creating just one   duplicate would be about 50   The   probability of one duplicate would be   about 50  if every person on earth   owns 600 million UUIDs   EDIT  Please also see JaredPar s comments

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Why not checking if the file exists   string fileName  do       fileName   System IO Path GetTempPath     Guid NewGuid   ToString       csv     while  System IO File Exists fileName

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This could be handy for you    It s to create a temp  folder and return it as a string in VB NET   Easily convertible to C    Public Function GetTempDirectory   As String     Dim mpath As String     Do         mpath   System IO Path Combine System IO Path GetTempPath  System IO Path GetRandomFileName      Loop While System IO Directory Exists mpath  Or System IO File Exists mpath      System IO Directory CreateDirectory mpath      Return mpath End Function

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You can also alternatively use System CodeDom Compiler TempFileCollection   string tempDirectory     c   temp   TempFileCollection coll   new TempFileCollection tempDirectory  true   string filename   coll AddExtension  txt   true   File WriteAllText Path Combine tempDirectory filename   Hello World      Here I used a txt extension but you can specify whatever you want  I also set the keep flag to true so that the temp file is kept around after use  Unfortunately  TempFileCollection creates one random file per extension  If you need more temp files  you can create multiple instances of TempFileCollection

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public static string GetTempFileName string extension      int attempt   0    while  true          string fileName   Path GetRandomFileName        fileName   Path ChangeExtension fileName  extension       fileName   Path Combine Path GetTempPath    fileName        try             using  new FileStream fileName  FileMode CreateNew             return fileName            catch  IOException ex              if    attempt    10          throw new IOException  No unique temporary file name is available    ex                 Note  this works like Path GetTempFileName  An empty file is created to reserve the file name  It makes 10 attempts  in case of collisions generated by Path GetRandomFileName

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Based on answers I found from the internet  I come to my code as following   public static string GetTemporaryFileName                string tempFilePath   Path Combine Path GetTempPath     SnapshotTemp        Directory Delete tempFilePath  true       Directory CreateDirectory tempFilePath       return Path Combine tempFilePath  DateTime Now ToString  MMddHHmm      -    Guid NewGuid   ToString       png        And as C  Cookbook by Jay Hilyard  Stephen Teilhet pointed in Using a Temporary File in Your Application    you should use a temporary file whenever you need to store information temporarily for later retrieval   The one thing you must remember is to delete this temporary file before the application that created it is terminated   If it is not deleted  it will remain in the user   s temporary directory until the user manually deletes it

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This is a simple but effective way to generate incremental filenames  It will look in the current directly  you can easily point that somewhere else  and search for files with the base YourApplicationName  txt  again you can easily change that   It will start at 0000 so that the first file name will be YourApplicationName0000 txt  if for some reason there are file names with junk between  meaning not numbers  the left and right parts  those files will be ignored by virtue of the tryparse call       public static string CreateNewOutPutFile                 const string RemoveLeft    YourApplicationName           const string RemoveRight     txt           const string searchString   RemoveLeft         RemoveRight          const string numberSpecifier    0000            int maxTempNdx   -1           string fileName          string    Files   Directory GetFiles Directory GetCurrentDirectory    searchString           foreach  string file in Files                        fileName   Path GetFileName file               string stripped   fileName Remove fileName Length - RemoveRight Length  RemoveRight Length  Remove 0  RemoveLeft Length               if  int TryParse stripped out int current                                  if  current  gt  maxTempNdx                      maxTempNdx   current                                  maxTempNdx            fileName   RemoveLeft   maxTempNdx ToString numberSpecifier    RemoveRight          File CreateText fileName      optional         return fileName

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In my opinion  most answers proposed here as sub-optimal  The one coming closest is the original one proposed initially by Brann   A Temp Filename must be   Unique Conflict-free  not already exist  Atomic  Creation of Name  amp  File in the same operation  Hard to guess   Because of these requirements  it is not a godd idea to program such a beast on your own  Smart People writing IO Libraries worry about things like locking  if needed  etc  Therefore  I see no need to rewrite System IO Path GetTempFileName     This  even if it looks clumsy  should do the job     Note that this already  creates  the file string filename1   System IO Path GetTempFileName      Rename and move filename   filename Replace   tmp     csv    File Move filename1   filename

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I mixed  Maxence and  Mitch Wheat answers keeping in mind I want the semantic of GetTempFileName method  the fileName is the name of a new file created  adding the extension preferred   string GetNewTempFile string extension        if   extension StartWith       extension       extension      string fileName      bool bCollisions   false      do           fileName   Path Combine System IO Path GetTempPath    Guid NewGuid   ToString     extension           try                       using  new FileStream fileName  FileMode CreateNew                   bCollisions   false                    catch  IOException                        bCollisions   true                      while  bCollisions       return fileName

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